Stabilized photographic silver halede



United States Patent STABILIZED PHOTOGRAPHIC' SILVER HALIDE EMULSIONSCharles F. H. Allen and Harry R. Beilfuss, Rochester,

N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., acorporation of New Jersey No Drawing. Application July 1, 1953, Serial.No. 365,541

5 Claims. (Cl. 95-7) This invention relates to fog-inhibiting agents.and stabilizers for photographic emulsions and to photographic emulsionscontaining them.

It, is well known that photographic emulsions on storage tend to losesensitivity and to become spontaneously developable without'exposure tolight. There. is normally a detectable amount of the silver salt reducedduring development in the areas Where no exposure was given; this iscommonly called fog, and sometimes called chemical fog where it isnecessary to distinguish between it and the efiects of accidentalexposure to radiation; in this invention, we are not concerned with thelatter.

Fog depends both on the emulsion and the conditions of development; fora given emulsion it increases, with the degree of development. Withconstant development conditions, it tends to increase with time,temperature and relative humidity of storage conditions; it is commonpractice to make accelerated tests of the stability of photographicemulsions by storage at increased temperature or humidity, or both. Itis of course desirable to have. emulsions as stable as possible underthe conditions of high temperature and humidity which may occur intropical climates, for example. Fog usually appears over the whole areaof the sensitive coating, but when severe, it frequently is non-uniform.Fog may also be caused by exposure to chemicals, for example, hydrogensulfide and other reactive sulfur compounds, hydrogen peroxide vapor,and strongly reducing materials. While anti-fog- 2,735,769 Patented Feb.21, 1956 such as methyl, ethyl, n-propyl, isopropyl, n-butyl, noctyl,n-decyl, n-octad'ecyl, etc., an aryl group, such as phenyl, 0-, m-, andp-tolyl, naphthyl, etc. (e. g. a mononuclear aromatic group of the.benzene series), or a heterocyclic group, such as furyl, quinolyl,benzothiazolyl, pyridyl, etc. In general, the compounds represented bythe above general formula can be prepared according to the methoddescribed in U. S. Patent 2,481,466, issued September 6, 1949. Themethod described in this patent consists in condensing a pyrazolonecompound containing a primary amino group in the 3- position togetherwith a diketene compound. Diketenes other than diketene itself can alsoadvantageously be employed in preparing the compounds of the above gen;eral formula.

The quantity of antifoggant or stabilizing compound employed inpracticing our invention is quite important in obtaining the resultsdesired.v This is due, in part, to the presence of the reactivemethylene groups as can be seen by reference to the above generalformula. Accordingly, the quantity of antifoggant or stabilizingcompound should not exceed 5 g. per mole of silver halide present in thephotographic emulsion. Amounts varying from 0.01 to 3 g. per mole ofsilver halide have been found to be particularly useful in practicingour in,- vention.

The fog inhibitors which 'We propose to use are added to the emulsionduring theprocess of manufacture, to avoid loss of sensitivity and toinhibit the growth of fog with passage of time under non-idealconditions of storage.

gants and stabilizers may protect, to some extent, against such effects,it is normally understood that an antifogga-nt protects againstspontaneous growth of fog during prolonged storage or storage at hightemperatures and humidities, or during development to maximum contrastand speed, or both. i

It is, accordingly, an object of our invention to provide a method forstabilizing photographic emulsions. A further object of our invention isto maintain the sensitivity and fog of silver halide emulsions at orclose to initial optimum values under keeping'conditions of hightemperature and humidity. A further object is to proide photographicsilver halide. emulsions containing antigpggants or stabilizers. Otherobjects will become apparent from a consideration of the followingdescription and examples.

The above objects are, in general, accomplished by adding to thephotographic emulsion certain organic compounds of the following generalformula:

wherein R represents an alkyl group, such as methyl, ethyl, n-propyl,isopropyl, etc., an aryl group, such as phenyl, o-, m andp-methoxyphenyl, o-, mand p-tolyl, etc. (e. g. a mononuclear aromaticgroup of the benzene series), or a heterocyclic group, such as furyl,quinolyl, benzothiazolyl, etc., and R1 represents an alkyl group,

A solution of the compounds of the invention when added in; suitableconcentration, before coating, to unsensitized, chemically sensitized,or optically sensitized photographic emulsions does not appreciablyaifect the? sensitometric values for sensitivity and fog whenmeasurements are made soon after coating. When sensitometricmeasurements are made at appreciable intervals of time, at elevatedtemperatures. and dry or somewhat humid conditions, these compounds dostabilize photographic speed and maintain fog at a low level.

The preparation of silverxhalide emulsions involves three separateoperations: (1) the emulsification and digestion or ripening of. thesilver halide, (2) the; freeing of the emulsion from excess solublesalts, usually by washing, and (3) the second digestion orafter-ripening to obtain increased sensitivity. (Mees: The Theory of thePhotographic Process, 1942.) We prefer to add the fog-inhibiting agentsafter the final digestion or afterripening, although they canadvantageously be added prior to digestion.

Listed below are a number of compounds coming within the scope of theabove general formula, which we have found to be particularlyadvantageous in practicing our invention. These compounds belong to agroup of compounds which we shall designate as triazaindenes.

1. H: CH:

3. 1% N 0=o J-d/H:

1,2,'3,5-tetrahydro-2,5-diketo-l,7-dimethyl-L4,7a-triazaindene 2. CH1;(luH 1,'2,3,5=tetrahydro-2,5-dlketoJ-methyl-1-phenyl-1,4,7a* v. itriazetndene-1,2,3,5-tetrahydro-2,5-di1reto-1,7-dipheny1-1,4,7a-triazaindeno olie 11:

1,2,3,5-tetrahydro-,5-diket0-7-o-methoxyphenyl-1-pl1eny1-1,4,7a-triazaindene1,2,3,5-tetrahydro-2,5-diketo-7-m-methoxyphenyl-1-phenyl-1,4,711-triazaindene H =0 CIHB1,2,3,5-tetrahydro-2,5-diket0-7-a-fury1-1-phenyl-1,4,7atriazaindene1,2,3,5-tetrahydro-2,5-diket0-7-methyl-'1-(2-quinolyl)- 1,4,7a-triazaindene H0 N C=0 O=\ N 1,2,3,5-tetrahydro-2,5-diketo-1-(2'benzothlazolyl) -7-methyl- 1,4,7a-triazaindene The photographicemulsions used in practicing our invention are generally of thedeveloping-out type; also, it is to be understood that photographicemulsions of varying halide content can advantageously be used. Theantifoggant compounds used in our invention have been found particularlyuseful when employed in conjunction with gelatino-silver bromiodideemulsions, although they can also be advantageously employed forstabilizing other silver halide emulsions, such as gelatino-silverchloride, bromide, chlorobromide, chlorobromiodide, etc. The emulsionscan be unsensitized, or sensitized with chemical sensitizers or opticalsensitizers. Sulfur sensitizers, such as those disclosed in Sheppard U.S. Patent 1,574,944 can advantageously be added to the emulsions intheconventional manner. Also, various gold sensitizers can be employedin the photographic emulsions stabilized according to our invention.

The efficiency of the antifoggant or stabilizing agent was determined byincubation of the emulsions for three days at a temperature of 120 F.and a humidity of 45 percent. The eflicieney was determined by measuringthe speed, gamma and fog of the incubated emulsions containing anantifoggant and comparing these measurements with those of the samebatch of emulsion before incubation. Also, similar measurements weremade on the same batch of photographic emulsion containing noantifoggant, both before and after incubation. The tests were made usinga high speed silver bromiodide emulsion exposed on an Eastman Type Ibsensitometer and developed for 6 /2 minutes in a developer of thefollowing composition:

grams N-methyl p-aminophenyl sulfate 1.5 Hydroquinone 1.3 Sodium sulfite(desiccated) Borax 4.5 Potassium bromide 0.4

Water to one liter Fresh Test Incubation Test Ex. Antiloggant g./moleNo. Compound AgX 10H 10 speed 7 Fog speed 7 Fog 1(a)-- None 3,800 0. 7510 2, 600 0.69 24 (0)...- Compound 6 0. 6 3, 450 0. 89 09 3, 350 0. 74l4 2(a) Same as 101).. (10.... Compound 5.. 0 6 3,600 0.73 08 3,500 0.72.12

In a manner similar to that illustrated in the above examples, othercompounds coming within the scope of the above general formula can beincorporated in photographic emulsions for the purpose of stabilization.The fog-inhibiting agents useful in practicing our invention can be usedin various kinds of photographic emulsions. In addition to being usefulin ordinary non-sensitized emulsions, they can also be used inorthochromatic, panchromatic and X-ray emulsions. If used withsensitizing dyes, they can be added to the emulsion before or after thedyes are added. Suitable dispersing agents for the silver halidecomprise gelatin, or other colloids, such as collodion, albumen,cellulose organic derivatives, synthetic resins, etc.

Instead of adding the fog-inhibiting agent directly to the photographicemulsion, it is sometimes desirable to incorporate the fog-inhibitingagent in a separate layer which is placed in contact wtih the silverhalide emulsion layer. Under such conditions, of course, it is desirableto use a higher concentration of fog-inhibiting agent than indicatedabove in the separate layer, which generally contains no silver halide.

We have also found that compounds selected from those of the abovegeneral formula wherein R represents a hydroxyl group can also be usedfor the purpose of stabilizing photographic emulsions. Such compoundscan be formulated in their keto form, or in their enol form.

For example, the compound having the following formula has been found tobe useful as an antifoggant.

2,5,7-triketo-l-phenyl-1,2,3,5,6,7-hexahydro-1,4,7a-triazaindene It willbe noted that the above compound has been written in its keto form. Alsosuch a compound can be written with a hydrogen atom of the methylenegroup being attached to one of the oxygen atoms of one of the keto.

Example 3.2,5-diketo-1-phenyl-7-(o-methoxyphenyl) -1,4,7a-triazaindene-c oorno 0.0.11 niN-o orn In a flask fitted with a 10-in. steam jacketedcolumn terminating in a still head fitted with a thermometer andconnected to a water cooled condenser, were placed g. (0.08 mole) ofethyl o-methoxybenzoylacetate and 35 cc. of xylene. The solution washeated to boiling, 8.75 g. (0.05 mole) of 1-phenyl-3-amino-5-pyrazolonewere added, and the mixture was heated for 1.5 hours, at 145-160 C. Thetemperature of the distillate varied between 7 5-95 C. while the waterand alcohol were distilling, and finally rose to 140 C. at the end ofthe reaction. The distillate collected (7.5 cc.) was a mixture of water,alcohol and xylene. On cooling the solution, the product crystallized.It was filtered and washed with alcohol, yield, 7.9 g.; M. P. 2l0212 C.

Example 4.2,5-diketo-1-phenyl-7-(m-methoxyphenyl) -1,4,7a-triazaindenehas This compound was prepared in a manner similar to Example 3, fromethyl m-methoxybenzoyl acetate and 1-phenyl-3-amino-5-pyrazolone. It wasobtained in a 65% yield,.M. P. 254255 C.

What We claim as our invention and desire secured-by Letters Patent ofthe United States is:

1. A photographic silver halide emulsion containing from 0.01 to 5.0 g.per mole of silver halide of a compound selected from those representedby the following general formula:

and

wherein R and R1 each represents a member selected from the groupconsisting of an alkyl group, an aryl group and a heterocyclic group.

2. A photographic silver halide emulsion containing from 0.01 to 3.0 g.per mole of silver halide of a compound selected from those representedby the following general formula:

wherein R and R1 each represents a mononuclear aromatic group of thebenzene series.

3. A photographic silver bromiodide emulsion containing from 0.01 to 3.0g. per mole of silver halide of a compound selected from thoserepresented by the following general formula:

wherein R and R1 each represents a member selected from the groupconsisting of an alkyl group, an aryl group and a heterocyclic group.

4.A photographic silver halide emulsion containing from 0.01 to 3.0 g.per mole of silver halide of a compound having the following formula:

CHaO

CQH5

5. A photographic silver halide emulsion containing from 0.01 to 3.0 g.per mole of silver halide of a com- 7 pound having the followingformula:

OCH1

GcHI 0=l\ -(5Hg References Cited in the file of this patent UNITEDSTATES PATENTS 2,350,138 Weissberger May 30, 1944' 2,449,225 Heimbach eta1 Sept. 14, 1948 2,450,397 Heimbach Sept. 28, 1948 2,481,466 BavleySept. 6, 1949 OTHER REFERENCES Wall: Photographic Emulsions. Pub. byAmerican Photographic Publishing C0,, Boston, 1929, pages 324 and 325.

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING FROM 0.001 TO 5.0 G.PER MOLE OF SILVER HALIDE OF A COMPOUND SELECTED FROM THOSE REPRESENTEDBY THE FOLLOWING GENERAL FORMULA: